This invention relates to cartons of the kind comprising an open-topped body with a cover hingedly connected thereto for the closure of the open top. The invention has been developed primarily for so-called "book pack" type cartons, that is to say cartons which are intended in their external appearance to resemble a book, the body including a base which extends outwardly beyond the walls of a rectangular body on three sides thereof, and a cover of similar size, so that the base and cover resemble book covers, the carton also including, at the remaining side of the body from which the base and cover do not project, a panel to resemble the spine of a book cover.
However, as will hereinafter become apparent, the invention is not limited in its applicability to such "book pack" type cartons.
Conventionally, "book pack" type cartons comprise a rigid rectangular inner component which forms the body proper, and an outer component which comprises the panels which form the base, cover and spine. Traditionally, the outer component is formed in the same way as a genuine hard back book cover, and comprises three panels of board each having a substantial thickness, e.g. around 1000 microns, which are hingedly connected together.
There are currently three methods of producing such a three panel outer book cover. Firstly a one-piece member of board about 1000 microns thick can be divided into the three panels by cutting away much of the thickness of the board, e.g. by routing, along the required fold lines. Secondly, instead of removing material in this way, such board can be creased along the fold lines. Thirdly, the three panels may be formed separately and jointed by a means of a layer of a facing material.
To achieve the required flexibility at the hinge, the thickness of the material which forms the hinge needs to be kept to a minimum yet have adequate strength. However, in a book pack type carton there is the additional requirement of attaching the outer component to the body, for which a secondary hinge piece is normally utilised. This increases resistance to bending at the hinge line.
The step of assembling the three boards requires considerable skill and as a result the product is expensive to manufacture. Even where the three panels are formed from a single member the step of locating the outer component accurately in relation to the inner member whilst they are secured together requires skill and accuracy such that a jig is normally required.
Substantial savings in time, cost and skill could be achieved if, instead of employing three separate boards, a one-piece blank could be used. However, the required strength for the base and cover panels has generally necessitated the use of relatively thick board, which cannot satisfactorily be folded so as to enable it to be made from a one-piece blank, and which in particular presents problems with regard to the construction of the hinge between the spine and cover panels because of the thickness and stiffness of the board material conventionally employed. If a sufficiently flexible hinge is to be achieved, the thickness of the board material along the intended hinge line must be very substantially reduced, leading to serious weakness at the hinge.